A magnetoresistive (MR) device is a device whose resistance changes in accordance with a change in magnetization. Almost every conducting magnetic material exhibits some magnetoresistance. However, the magnetoresistive effect is particularly large in certain materials such as permalloys, which are nickel-iron (NiFe) alloys, and other ferromagnetic materials such as Co, Ni, and Fe alloys. Magnetoresistive devices respond to magnetic fields, and provide signals that typically are significantly more than that achieved with Hall sensors. A class of magnetoresistive devices with a larger sensitivity than standard magnetoresistive devices is known as giant magnetoresistive (GMR) devices. A random access memory that uses magnetoresistive films is generally referred to as a magnetoresistive random access memory (MRAM).
In an MRAM, a triple-layer structure having two ferromagnetic layer structures separated by a thin non-magnetic layer therebetween form a basic memory device. One of the ferromagnetic layer structures is used to store (write) information and the other of the ferromagnetic layer structures is used to sense (read) the stored information.
Typically, giant magnetoresistive devices are realized by choosing the thicknesses of the ferromagnetic thin-films and the intermediate layers in “sandwich” structures. Such devices, with the giant magnetoresistive effect, yield a magnetoresistive response that can be at least an order of magnitude greater than that associated with anisotropic magnetoresistive devices.
The magnetization of the ferromagnetic layers in giant magnetoresistive memories can be intended to be uniform. However, under certain conditions, the magnetization can become non-uniform. This non-uniformity can reduce the repeatability of the switching that occurs during writing of information to the giant magnetoresistive device which, in turn, reduces the reliability of the giant magnetoresistive memory.
The present invention is directed to an arrangement for increasing the uniformity of the magnetization of the ferromagnetic layers in giant magnetoresistive memories.